The present invention relates to contact lens care compositions useful in treating hard contact lenses. The compositions of the present invention involve an unique polymer gelling system comprising a galactomannan polysaccharide and a borate crosslinking compound, which together form a mucin-like soft gel in the presence of increasing pH and ionic strength.
Hard contact lenses are named for their rigidity, and are generally made of polymethyl metliacylate (PMMA), siloxane acrylates, fluoro-siloxane acrylates or fluoro polymers. The most common type of hard contact lenses are the rigid gas permeable ("RGP") lenses, which allow soluble gases contained in natural or artificial tears to pass through it and feed the corneal tissues.
Hard contact lenses require periodic cleaning and disinfecting before they can be reused by the wearer. Numerous cleaning, rinsing, disinfecting and storing solutions have been used in the past. In general, these solutions have contained one or more antimicrobial agents, salts, buffers, surfactants and conditioning agents. Conditioning agents are useful in hard contact lens care solutions because they assist in lubricating the lenses. When hard contact lenses are inserted in the eye they can cause discomfort to the user due to the relatively hydrophobic surface and rigid nature of the lenses. Thus, cleaning and conditioning solutions which provide lubricating conditioners are particularly useful in hard contact lens care. Conditioning compositions often are multi-functional solutions designed to be used for wetting, soaking and disinfection of hard contact lenses.
Hard contact lenses have limited water retention capability and do not wet adequately when placed in solutions or inserted in the eye. Current technology teaches that the application of natural or synthetic water soluble polymers to the surfaces of hard contact lenses not only increases the wettability of the lenses, but also provides a "cushion" layer between the lens and the eye. These polymer adsorptions have been equated with increased wettability as well as user comfort and tolerance. Dissipation of the "cushion" layer, however, occurs rapidly in most prior art constructions, since there is little specific interaction between the mobile polymer in this layer and the lens surface. As a result, the wearer begins to feel discomfort and must rewet the lens surface.
Surface-active agents have been employed in conditioning solutions in an attempt to alleviate the above-described problems. Surface-active agents are adsorbed on the lens surface and allow ready spreading of tears when the lenses are inserted, thus making them more comfortable to wear. Representative wetting agents and viscosity modifiers have included: cellulose derivatives, such as cationic cellulosic polymers, hydroxypropyl methylcellulose, hydroxyethylcellulose and methylcellulose; polyols, such as polyethylene glycol, glycerine and polyethylene oxide (PEO) containing polymers; polyvinyl alcohol; and polyvinyl pyrrolidone. Such additives may be used in a wide range of concentrations as is known in the art. These types of agents, however, do not adsorb to a significant level to the lens, and therefore do not provide prolonged comfort.
Polymers which provide a more prolonged comfort level typically need to be employed in high concentration to create a higher viscosity, and thereby prolong the retention of the polymer. The use of these high viscosity agents, however, may cause blurring of vision when the lens is first placed in the eye, and also creating a sticky feeling of the lens to the user, making lens insertion and handling difficult. More hydrophobic polymers can adsorb more readily to the lens, and can be formulated at lower concentrations to provide better lubrication. The disadvantage, however, of a more hydrophobic polymer is that the polymer may also act as a substrate for deposits and as a consequence, make the lens more prone to filming and lipid deposit.
Various cleaning, disinfecting and storing solutions have been described in the art. For example, the use of antimicrobial agents like quaternary amonionium polymers, and particularly, polyquaternium-1, have been described in U.S. Pat. No. 4,407,791 (Stark) and U.S. Pat. No. 4,525,346 (Stark). U.S. Pat. No. 4,758,595 (Ogunbiyi) and U.S. 4,836,986 (Ogunbiyi) have described the use of polymeric biguanides in disinfecting solutions. Various contact lens care solutions containing lubricants for conditioning hard contact lenses have also been disclosed in the patent literature. For example, U.S. Pat. No. 4,436,730 (Ellis et al.) discloses compositions for wetting, soaking and lubricating lenses, and U.S. Pat. No. 4,820,352 (Riedhammer et al.) and U.S. Pat. No. 5,310,429 (Chou et al.) disclose compositions for cleaning and lubricating lenses.
Various gelling compositions have been described in the art for use in ophthalmic applications. In general, these types of systems have been used for the topical application of pharmaceuticals, wherein the topical solution partially or fully gels upon instillation in the eve, to allow for a sustained release of the pharmaceutical agent to the eye. Such agents have included the use of polyvinyl alcohols, euchema gels, xanthan gums and gellan gum. However, stimuli sensitive polymer systems for treating contact lenses have not been disclosed in the art.
The use of current gelling systems have a number of drawbacks for use in contact lens care applications. U.S. Pat. No. 4,136,173 (Pramoda, et al.) and U.S. Pat. No. 4,136,177 (Lin, et al.) disclose the use of therapeutic compositions containing xanthan gum and locust bean gum which are administered in liquid form and gel upon instillation. These disclosures describe a mechanism for transition from liquid to gel involving pH change. pH sensitive gels such as carbomers, xanthan gellan, and those described above, need to be formulated at or below the pKa of their acidic groups (typically at a pH of about 2 to 5). Compositions formulated at low pH, however, are irritating to the eye. U.S. Pat. No. 4,861,760 (Mazuel, et al.) discloses ophthalmic compositions containing gellan gum which are administered to the eye as non-gelled liquids and gel upon instillation due to a change in ionic strength. These systems do not involve the use of small cross-linking molecules, but instead provide gel characteristics due to self cross-linking during ionic condition changes.
Current polymer gel systems, however, have a number of disadvantages. Contact lens conditioning solutions are typically formulated as multi-functional compositions which disinfect and condition the lens simultaneously. These multi-purpose solutions will typically employ an polymeric cationic antimicrobial agent. Anionic polymers electrostatically interact with polymeric cationic antimicrobials, such as polyquaternium-1 and PHMB. This interaction interferes with the disinfecting activity of the antimicrobial agents, and the disinfecting efficacy of the solutions may therefore be compromised. Ion sensitive gels such as gellan, carageenan and xanthan are capable of forming gels when they are used at a relatively high viscosity (high concentration) of about 100 to 1000 centiposes ("cps"). This viscosity range, however, is generally too high for case of lens handling and visual clarity.
Gels involving the cross-linking of polysaccharides with borates are disclosed for use as well fracturing fluids in U.S. Pat. Nos. 5,082,579, and 5,160,643. These patents describe the use of borates and polysaccharides for industrial oil well excavation.
The use of other gelling systems for contact lens care applications also have a number of drawbacks. For example, natural polymers such as xanthan gum have the disadvantage of lot to lot variability due to variations in source and/or limited manufacturing controls during processing. These variabilities cause significant undesirable changes in the properties of the compound, such as variable gelling characteristics. Thermogelling systems such as polyethylene oxide/polypropylene oxide block copolymers ("PEO/PPO") lose water in order to form gels, and consequently result in turbid gels.
Polyvinyl alcohol-borate crosslinking gels have been disclosed in U.S. Pat. No. 4,255,415 (Sukhbir et al.) for ophthalmic drug delivery. These compositions are pre-formed gels, and are therefore difficult to dispense. WIPO Publication No. WO 94/10976 (Goldenberg et al.) discloses a low pH PVA-borate delivery system that does go through liquid/gel transition. This system has the disadvantage. however, of limited gelling effects, and only at certain concentrations of PVA depending on the molecular weight of the PVA utilized. Furthermore, since the crosslinking cites are unlimited with this system, strong local gelation upon addition of base has limited its manufacturing and, therefore, polyvinyl pyrrolidone presumably has been included in these compositions to overcome the shortcoming. The novel gelling system of the present invention does not have the above limitation.
What is needed, therefore, are rinsing, disinfecting, cleaning, storing and conditioning solutions for hard contact lenses which provide the necessary cleaning, disinfecting rinsing, storing and conditioning efficacies and which provide ease of handling and comfort to the user when the lenses are inserted in the eye and worn.